Process and device for the detection of cracks in riveted joints using an eddy current probe

Abstract

The present invention relates to a process and device for the non-destructive examination of riveted joints or the like, particularly for monitoring the fuselage of an aircraft. According to the invention, an eddy current probe is used and two rectangular components of the signal of unbalance from the latter are compared with thresholds predetermined by prior measurements on similar new joints, in order to determine the presence and/or the absence of cracks.

What is claimed is: 
     
       1. A device for the non-destructive examination of a succession of riveted joints aligned along an X--X axis and orthogonal to a Y--Y axis and spaced equidistantly apart, comprising: an eddy current probe comprising a central primary injection winding surrounded by four peripheral secondary detection windings, said secondary windings being angularly distributed equally on the same circle centered on the primary winding and disposed in two's along two right-angled diameters (X--X and Y--Y), one of the said diameters (X--X) being adapted to merge with said aligned succession of riveted joints, two diametrically opposite said secondary windings being of the same direction, but of direction opposite the other two said secondary windings and the four said windings being connected in series so that two consecutive windings are of opposite direction;   means for advancing said probe along said X--X axis;   said probe being linked with means for controlling and reading said probe, said means for controlling and reading said probe and said probe generating a cyclic signal when said probe is advanced along said succession of aligned riveted joints, said cyclic signal having a first shape that extends parallel to said X--X axis when one of said riveted joints being examined does not include a crack, and a second shape that extends both parallel to said X--X axis and parallel to said Y--Y axis when one of said riveted joints being examined includes a crack, said controlling and reading means for said probe generating an X component of said cyclic signal in phase with said X--X axis and a Y component of said cyclic signal in phase with said Y--Y axis as said probe is moved along said X--X axis in a direction orthogonal to said Y--Y axis;   memory means for storing a first threshold and a second threshold, said first threshold being measured along said X--X axis such that when said X component is in excess of said first threshold, the presence of at least a riveted joint is detected, and said second threshold being measured along said Y--Y axis such that when said Y component is not in excess of said second threshold the presence of a riveted joint that does not include a crack is detected;   said means for controlling and reading said probe further continuously measuring said components of said cyclic signal;   means for comparing said components with said first and said second threshold having a comparison output; and   means for recording said comparison output.   
     
     
       2. The device as claimed in claim 1, wherein the distance separting said primary injection winding from any of said secondary detection windings is equal to half a distance separating two consecutive riveted joints in said aligned succession of riveted joints. 
     
     
       3. The device as claimed in claim 1, further comprising means for displaying said comparison output. 
     
     
       4. A process for the non-destructive examination of a succession of riveted joints aligned along an X--X axis and othogonal to a Y--Y axis and spaced equidistantly apart, comprising: using an eddy current probe comprising a central primary injection winding surrounded by four peripheral secondary detection windings, said secondary windings being angularly distributed equally on the same circle centered on the primary winding and disposed in two's along two right-angled diameters (X--X and Y--Y), one of said diameters (X--X) being adapted to merge with said aligned succession of riveted joints, two diametrically opposite said secondary windings being of the same direction, but of direction opposite the other two said secondary windings and the four said windings being connected in series so that two consecutive windings are of opposite direction;   advancing said probe along said succession of riveted joints;   linking said probe with means for controlling and reading said probe;   generating a cyclic signal with said probe and said means for controlling and reading said probe during said advancing of said probe, said cyclic signal having a first shape that extends substantially parallel to said X--X axis when one of said riveted joints being examined does not include a crack, and a second shape that extends both parallel to said X--X axis and parallel to said Y--Y axis when one of said joints being examined includes a crack;   generating an X component of said cyclic signal in phase with said X--X axis and a Y component of said cyclic signal in phase with said Y--Y axis during said advancing of said probe along said X--X axis in a direction orthogonal to said Y--Y axis;   recording a plurality of signals having said first shape by examining with said probe a large quantity of control riveted joints similar to said succession of aligned riveted joints being examined, said control joints not including any cracks;   generating an envelope of signals from said plurality of signals having said first shape and determining a first threshold measured along said X--X axis such that when said X component of said cyclic signal is in excess of said first threshold, the presence of at least a riveted joint is indicated;   determining a second threshold measured along said Y--Y axis such that when said Y component of said cyclic signal is not in excess of said second threshold the presence of a riveted joint that does not include a crack is indicated;   thereafter advancing said probe along said succession of aligned riveted joints to be examined and continuously measuring the components of said cyclic signal;   comparing said cyclic signal components with said first and said second thresholds, in order to indicate the presence of riveted joints that do not include any cracks; and   recording the results of said comparing said components of said cyclic signal with said thresholds.   
     
     
       5. The process according to claim 4 further comprising the step of displaying the results of said comparing said components of said cyclic signal with said thresholds.